Fusion-joining coarse-surfaced high carbon ferrous metals to metals



United States Patent l 3,380,151 FUSION-JOINING COARSE-SURFACED HIGH CARBON FERROUS METALS T0 METALS Richard Parsons, New York, N.Y., assignor to Oakite grorliucts, Inc., New York, N .Y., a corporation of New or No Drawing. Filed Feb. 9, 1962, Ser. No. 172,117 14 Claims. (Cl. 29-488) This invention concerns the joining, i.e., by brazing, soldering, or Welding, metal parts which can be brazed, soldered or welded, to high carbon content ferrous metals which ordinarily have coarse surfaces, such as cast iron as grey cast iron, malleable iron, and wrought iron.

The high carbon content ferrous metals such as cast iron as grey cast iron, and malleable iron and wrought iron ordinarily, that is to say when clean (e.g., free of molding sand or scale) and before being surface ground or polished, have a coarse surface, apparently because of their coarse grain structure as distinguished from that of the low carbon steels which are easily rolled and shaped.

Accordingly, the said coarse-surface high carbon ferrous metals, and included among them those which also have high silicon content such as the acid-resistant ferrous metals as the one long known by its trademark Duriron," conveniently can be called ferrous metals ordinarily having a coarse surface or singly an ordinari- 1y coarse-surfaced ferrous metal.

Since such joining operations as brazing, soldering, and welding generally include fusion and subsequent solidification of either a solder or at least part of the base metal along the joint, or fusion of a flux, these joining operations conveniently are referred to jointly herein as fusion-joining or flux-joining.

Thus, the various metals which can be joined by fusion-joining can be called fusion-joinable metals. When such a metal is fusion-joined to a metal of a different class, such as copper or brass so called the fusion junction.

The method of the invention then applies more particularly to fusion-joining a fusion-joinable metal to an ordinarily coarse-surfaced ferrous metal, with which such fusion-joining operation heretofore could not be accomplished or at best could be carried out only by undesirable methods involving considerable hazard and expense and yielding only erratic results.

Briefly then, the invention is that of fusion-joining a fusion-joinable metal to an ordinarily coarse-surfaced high carbon content ferrous metal by applying to the latters surface where such joining is to be done, a firmly adhering, substantially continuous, at least masking electrodeposit of nascent iron, and then fusion-joining the fusion-joinable metal part to the thus nascent iron electroplated surface of said ferrous metal.

In the description firmly adhering, substantially continuous, at least masking for the electrodeposit of nascent iron, the expression firmly adhering means that the deposit adheres to the ferrous base metal without flaking and is non-peeling in that it cannot be peeled off from the ferrous metal base.

Then the expression at least masking means that the deposit is at least thick enough at least to mask the generally overall finely spotted or matted surface of the ordinary coarse surface of the high carbon content ferrous metal to the extent that the finely spotted or matted appearance is replaced by a substantially uniform apparently silvery-grey clean iron surface color.

The invention includes also as a product the thus fusion-joined article of manufacture which comprises an 3,380,151 Patented Apr. 30, 1968 ordinarily coarse-surfaced high carbon content ferrous metal, a fusion-joinable metal fusion-joined to it at a fusion-junction, and nascently deposited iron within the fusion junction.

Heretofore, considerable difiiculty was encountered in trying to accomplish practical fusion-joining with an ordinarily coarse-surfaced ferrous metal. For example, it has been substantially impossible dependably to fusion-join a metal, except to a limited extend and under special conditions, to such ordinarily coarse-surfaced ferrous metal, especially cast iron such as grey cast iron.

To a limited extent, for example, brazing has been carried out with some high carbon content ferrous metals. However, such operation required first subjecting the .such ferrous metal base article to a special pre-treatment in one of a few proprietary molten inorganic cleaning and descaling baths. This involves initially preparing the surfaces of the metal products for the fushion-joining operation by immersing them, for example, in a catalyzed molten salt reduction bath (having a melting point of about 500 F.) and at an operating range of 850-950" F., and passing a direct current from an anode through the molten bath to a cathode.

Not only is such a procedure overly costly due to the energy required to maintain the bath molten, but also it is highly hazardous to the operators working about such bath, for example, from dragout on the articles leaving such hot bath; yet, in addition the results are inadequate. Thus, there appears to be a lack of uniformity in the treatment, for the percentage of rejects is undesirably too high for general practical operation; and all too often the resulting brazed joints are inadequate as manifested, for example, by a high percentage of leaks.

The foregoing disadvantages and others are overcome by the process of the invention, which is a significantly less costly, relatively quicker, and considerably safer method of fusion-joining, and provides a resulting more regularly and uniformly dependable product.

Considered broadly, the process of the invention is a method of fushion-joining a fusion-joinable metal to an ordinarily coarse-surfaced high carbon content ferrous metal, which comprises removing from at least the portion of the surface of said ferrous metal which will be included in the fusion-junction any soil and rust which initially should be removed, depositing on at least said portion of the surface of the ordinarily coarse-surfaced ferrous metal a firmly adhering, substantially continuous, at least masking electrodeposit of nascent iron; and thereafter fusion-joining a fusion-joinable metal to at least that thus nascent iron electrodeposit masked portion of said ferrous metal. The masking electrodeposit is essentially pure carbon-free iron.

The method of the invention can be carried out, and its product produced, by producing the firmly adherent, masking electrodeposit of nascent iron on the coarse-surfaced ferrous metal by any practically satisfactory method of electrodepositing such a deposit of iron. Obviously, before starting the electrodeposition, any soil or rust, particularly on the specific area which will be in the fusion junction, should be removed.

Where necessary, that can be done separately by any of the respectively suitable available methods, depending on the nature and extent of the soil. In many cases, wherein the residual molding sand or oil or grease, or rust are can be operated to give such firmly adhering masking deposit. Effective as such iron plating bath is any of a wide variety of aqueous acid baths having dissolved therein various effective amounts of one or more sequestering agents which form water-soluble chelates with iron whether ferrous or ferric, along with an efiective concentration of an alkali metal hydroxide, such as sodium or potassium hydroxide .or ammonium hydroxide, but below that which would make the bath alkaline.

Applicable sequestering agents include the polyalkylene polyamine polyacetic acid compounds and their monoand divalent metal salts, for example, diethylenetriamine pentaacetic acid and any of its alkali metal and ammoniu'm salts-or even any of its alkaline earth salts as its ca'loium or magnesium salts, and any of the mono-hydroxyethyl-tetra-carboxymethyl diethylenetriamines or dihydroxy ethyl tricarboxymethyl diethylenetri'amines, and any of the corresponding sa'me salts of any of them, as well as any of the free acid and salt form sequestering agents disclosed in US. letters Patents 2,831,885, 2,848,469, 2,859,104, and 2,906,762.

Additional effective sequestering agents are the various monohydr-oxy or polyhydroxy, monoor polycarboxy lower aliphatic acids having from two through seven carbon atoms such as citric acid, tartaric acid, gluconic acid,

glucoheptonic acid, and its isomers gal'actoheptonic acid,

fructohe'p'tonic acid, and the mixed hexahydroxyheptoic acids, and saccharic acid, or an amino, polyhydroxy lower aliphatic acid such as 3amino-2,4,5,6,7-pentahydroxy hept-oic acid, as well as the alkali metal and ammonium salts of any of those acids and the alkaline earth (including magnesium with them) salts of any of those polycarboxylic acids.

While individual baths can be prepared using any one of the foregoing and other effective sequestering agents along with a suitable amount of alkali metal hydroxide to give an effective pH value not exceeding 7, more than one of any applicable sequestering agents can be used. There can be included various amounts of ethylenedianiine tetraacetic acid or of any of its monoto tetra-alkali metal or ammonium salts as Well as any of its alkaline earth metal salts (including magnesium among them), and generally to the extent of no more than about one-half the amount of other sequestering agent, or of a lower alkanolamine such as mono-, di-, or triethanol-amine and like propanolamines.

Also any of the various six or seven carbon atoms polyhydroxy acids or any of the sugar acids can be admixed with one another or with any of the other sequestering agents, and advantageously with from about one-third to three times its quantity of a hexitol as sorbitol or mannitol.

Effective aqueous acid baths can be prepared with some one or more of the free acid sequestering agents of those mentioned above and/ or with some relatively neutral water-soluble salts of any of them, to provide a bath having such pH below 7, between which the specific sequestering agent or agents used can form a complex with iron. Such acid baths can include also various amounts of an alkali metal or ammonium dihydrogen phosphate such as monosodium or monopotassium dihydrogen phosphate.

For more effective iron plating with an acid bath, its pH can be in the range under 7 to about pH 3.5. A bath can be prepared with pH as low as 3.0 to 3.2, at which a suitable iron electrodeposit can be obtained. However, at such low level with many of the acid baths the plating rate may be too slow and the throwing power relatively poor. The minimum for generally practical operation should be at least about pH 3.5, and generally preferably at least about 4.0.

When the preliminary cleaning is not going to be conducted in the plat-ing bath, it is desirable that it contain in solution at least some small amount of a compatible iron salt or chelate, which is soluble at the pH of the aqueous bath. It is advantageous also to use some suitable iron bearing anode. Thus generally, the starting composition of the bath need contain only very little of the watersoluble iron compound such as an iron salt or chel-ate, if the bath will not be used to clean the coarsefisurfaced ferrous metal which is to be given the iron ele'ctrodeposit.

To provide then the initial iron content of the bath, it can contain a very small amount such as one-tenth percent or even less of such water-soluble iron salt as a ferrous or a ferric salt, soluble at the pH of the bath, such as ferrous or ferric sulfate, chloride, acetate or nitrate, as well as any of the iron chelates of any of the applicable sequestering agents and soluble at the pH of the bath at least to the extent merely .suflicient to initiate therein electrodeposition of iron.

As already indicated, initial content of such iron salt or chelate can be avoided when the bath is to be used for the preliminary cleaning of the coarse-surfaced ferrous metal which is to receive the iron electrodeposit. That is so because such preliminary cIeaning conducted by direct current from iron-containing anodes, and preferably by periodic reverse current procedure, to affect such preliminary cleaning, results in providing an adequate initial amount of dissolved iron in the bath sufficient to enable electrodeposition of iron on the cathode to progress by continued dissolution of iron from the particular iron-containing anode used to enable depositing the necessary firmly adhering, at least masking electrodeposit of iron on the 'originally coarse-surfaced ferrous metal cathode.

Where such cathode initially is clean and an iron salt or chelate soluble in the bath is not available or will not be used for some reason, suitable amount of scrap iron can be suspended or immersed in the bath to be acted on by the bath under direct, and preferably by periodic reverse, current thereby to enable dis-solving into the bath sufiioient iron necessary to permit electrodeposition of iron on the cathode thereafter to continue with accompanying dissolution of iron from the iron containing anode.

Ordinarily after some use of an aqueous acid bath, especially starting at a low pH as near 3.0, its pH increases as a result of dissolution of iron from the ironcontaining anode. That can enable preparing, if neces sary, a bath with an initial pH of as little as say 3.2 if the working load or other conditions do not make it unsatisfactory to operate the bath through what may be called a breaking in period while the pH rises to 3.5 or 3.6 or so.

For regularly dependable deposition of iron, the total dissolved solids in the bath can range from about one to about five pounds per gallon (i.e., about to about 600 grams per liter). A generaly good practical concentration, bearing in mind such factors as conductivity, plating rate, and dragout is in the neighborhood of two pounds per gallon. However, for higher conductivity with certain solutions (e.g., sodium gluconate without any other added salts, having a pH of about 6.5), it is more desirable to work with solutions of about four pounds per gallon.

The concentration of the sequestering agent, whether a single one or a mixture of them, can vary widely, generally from about two to about one hundred percent of the total solids content, and preferably from about five to about ninety-five percent of it, depending on providingt-he required pH value or range.

Grey cast iron, or black iron or other cast iron is very satisfactory for anodes of the ferrous material to replenish iron to the bath as it is plated out to provide a consistently uniform iron electrodeposit on the initially coarse-surfaced ferrous metal cathode. Electrolytic iron anodes also are suitable and at times even cold rolled steel anodes can be used. To avoid interference with the quality of the iron deposit by suspended carbon particles released from a high carbon content ferrous metal anode over continued use, it is desirable to enclose such anodes in Orlon or other suitable anode bags, as preferable over filtration of the bath.

Consideration should be given to the relationship of anode area to that of the articles being plated and thus serving as cathodes. Generally, it is advisable that the anode area be significantly greater than that of the part to be plated, and even up to double its area particularly if the cathode part has deep hollows.

The bath may be operated over a wide temperature range, for example, from as low as ambient (i.e., room) temperature. However, the plating rate then is very slow (e.g., at about 80 F.) and the voltage needed for suitable current density is excessive, being from 12 to 15 volts, or even more. A presently indicated most practical temperature range is from about 140 to about 180 F., although there is no discernible difference in the adhesion and generally desirable character of the iron electrodeposit even at the lower temperatures. Where conditions permit, very satisfactory practical results are obtained even at 200 F. and can be obtained also at possibly even a higher point. It appears generally advisable, of course, to work safely below the boiling point.

Current density, for generally good results, should range from about to about 80 amperes per square foot, and under many conditions can be as high as 100 amperes per square foot. However, for cathode articles having sharp points or projections, it may be advisable to operate somewhat under 80 amperes per square foot to avoid burning.

Thus, the maximum current density for any particular bath should be just under that at which the electrodeposit would begin to show signs of burning. However, the current density generally would have to be well over 100 amperes per square foot before any indication of burning or other undesirable injury can occur to the iron deposit on the coarse-surfaced high carbon content ferrous metal article cathode, or produce a flaky (and thus undesirable) electrodeposit.

The method of the invention is operable readily in quantity production scale. As already indicated, rust and some soils can be removed by subjecting the articles in the acid plating baths to preliminary electrolytic treatment, including periodic reverse current, for a time sufficient to remove soil and rust. That will depend on the type and extent of soil and rust, the bath, and the treatment. 1

For some combinations of these conditions, including mild soil and/or rust, two or three minutes of reverse current treatment may be adequate. Slightly heavy soil and rust, possibly may need from about ten to almost fifteen minutes. For heavy soil, oil or grease and/or rust conditions, up to about thirty minutes or so may be required.

For some soils, perhaps more so with oil and grease it can help to include a small percent, generally under one-half percent and possibly more often about half of that or less, of a synthetic detergent, nonionic or anionic and at times even cationic, or a mixture of any of them, as specific conditions may dictate.

As stated above, the iron electrodeposit need be merely sufficient to mask the coarse, generally grainy surface appearance. Because of the generally rough and irregular surface of the base coarse-surfaced ferrous metal base, in that it is not flat and smooth as in the case of low carbon steel, no specific numerical minimum thickness can be stated. Thus, with cast iron or any other coarsesurfaced ferrous metal, the deposit thickness appears to be adequate when the original (cleaned) surface is covered with the iron electrodeposit to the extent that the plated surface, at least over the area which will be in the fusion junction, appears to be covered by an overall substantially continuous electrodeposit of iron.

Such minimum deposit then being sufficient to resist being destroyed or burned away by oxidation under the flame used in the joining operation, as a single such simple test if needed can show, is adequate to enable dependable fusionjoining then to be accomplished with the particular coarsesurfaced ferrous metal.

Ordinarily, the electrodeposit thickness does not have to be much more than that just described above, even though the thus plated surface then may not be entirely flat. A slightly thicker deposit even below 0.0001 inch could be more practical. However, it is difiicult also to set a numerical maximum thickness applicable to all surfaces of the various coarse-surfaced ferrous metals. While up to about 0.0001 inch thick might be more than enough for most conditions, yet, where particularly desired, it could be as much as up to about 0.0002 inch thick. Generally, there does not appear to be any particular need to plate a deposit thicker than that.

While the method of the invention is applicable to fusionjoining of any coarsely-surfaced ferrous metal, it is ap plicable particularly to fusion-joining to cast iron such as grey cast iron. Accordingly, the invention will be more fully illustrated below, but is not intended to be restricted, by a description of details of its application to fusionjoining to grey cast iron. It applies equally to fusionjoining with any other coarse-surfaced high carbon content ferrous metal.

Cast iron castings, for example, of a manifold (5 inches long by 5 inches high by 2.5 inches wide) for a liquid heat exchanger were cleaned of any adhering loose mold sand, in customary manner. One end has an opening to be threaded to receive a one inch outside diameter threaded input line. In one side at the other end, there were counter-bored three non-threaded holes around each of which there is to be fusion-joined a one-half inch outside diameter copper outlet line.

These manifolds then were suspended suitably spaced from one another by inserting a hanger hook of a cathode rack into the one inch bore at one end of each of them respectively. As thus suspended, they were immersed,

properly spaced from grey iron anodes (of about double the cathode area), in an aqueous acid iron plating bath held at 200 F. and containing per liter 195 grams of citric acid and 45 grams of sodium hydroxide, all as described in bath (b) below.

Since these cast manifolds were oily and dirty, and rusted in areas, they were subjected in this bath for fifteen minutes to periodic reverse current of five seconds direct current tothe cathode, and ten seconds the reverse, to clean them. Without removing them from this bath, direct current (set to deliver amperes per square foot of cathode area) then was passed from the anodes to these manifolds as cathodes to deposit iron on them for fifteen minutes. The castings then were removed, rinsed adequately with hot water and allowed to air dry. They showed a continuous and uniform electrodeposit of iron completely masking the original spotted cast grey iron surface.

Then a clean end of each of the three one-half inch O.D. copper tubes was dipped in flux and brazed to the counterbored opening for it in the manifold, by placing a silver solder ring (with half inch CD.) at each such counterbored hole, inserting the fluxed end of the copper tube in the silver solder ring, and flame-fusing it around th junction in the usual manner.

Such completed manifold tested under high water pressure shows no leaks in any part of the fusion-joint around any of the copper tubes thus fusion-joined to the cast grey iron manifold.

Splitting the copper tube by sawing down through its axis and also likewise through its counter-bore in the casting and then separately gripping the copper of each half near its fusion junction and pulling it, towards its axis, away from its part of the casting, exposed an adhering continuous (unbroken) semi-circular portion of the solder outside that end of each half of the copper tube and in its half of the counter-bore. Thus, the absence of any break in each such residual semi-circular portion, which otherwise would expose an originally solder covered area where no fusion-joining occurred, showsv that with the applied iron electrodeposit the brazing took hold around that entire counter-bore.

Any of the various reverse current cleaning and combined bath operating conditions in the foregoing more fully described illustrative operation can be changed at least within the ranges disclosed ahead of that description, to be practical. So also the same bath at any combination of suitable operating conditions can be use-d to clean and plate a corresponding iron electrodeposit on any other such castings of the same or any other coarse-surfaced high carbon ferrous metal of the type disclosed herein.

As already stated above, the already described electrodeposition of iron can be carried out in any acid iron plating bath, illustrated by, but not restricted to, the following:

That quantity of gluconic acid was provided by using 240 grams per liter of a commercially available aqueous solution containing 50% gluconic acid. The bath pH is 3.5.

Grams per liter Citric acid 195 Sodium hydroxide 45 In this bath (having pH 3.6), the sodium hydroxide neutralizes part of the citric acid so that the composition of the bath actually is about 120 grams each of sodium citrate and citric acid.

Grams per liter Sodium diethylenetriamine pentaacetate 180 Monosodium dihydrogen phosphate 60 The pH is 6.6. The pentaacetate Was used as a 34% aqueous solution.

The sodium hydroxide of bath (b) can be replaced by any other herein indicated applicable alkaline agent or even compatible amine, e.g., diethylamine or an, ethanolamine and their content varied up or down so long as the bath pH still is below 7 and above about 3.2 and preferably at least about 3.5.

The sodium citrate resulting from the neutralization in bath (b) can be added directly as sodium, or can be replaced by and added as some other alkali metal or ammonium, citrate without any noticeable difference, or even by a compatible amine salt of it as indicated in the preceding paragraph.

The gluconic acid of bath (a) and citric acidof bath (b) can be replaced in whole or part by any quantity of the other of them or of any other hereinabove disclosed acid sequestering agent which is sufficiently soluble in water for the pH of the bath to be within the recently above indicated acid range.

The sodium diethylenetriamine pentaacetate can be replaced in whole or part by its corresponding salt of any other alkali metal or its ammonium or above indicated amine salt, or by the correspondingtetrm, tri-, di-, or mono-acetate, or even of ethylenediarnine pentaacetic acid itself or by any other neutral or acid sequestering agent sufficiently soluble in Water for the pH of the bath to be within the above disclosed acid range.

The sodium dihydrogen phosphate can be replaced in part or as a whole by any other alkali metal or ammonium dihydrogen phosphate or even by a water-soluble lower alkyl (with l3 carbons) acid phosphate or a watersoluble alkali metal, ammonium, or amine (as above indicated) acid salt of such alkyl acid phosphate with up to about 18 carbon atoms in the alkyl chain, and so long as the concentration of any of them keeps the pH of the bath under 7.

The throwing power of these acid baths in many instances may not be as high as that of an alkaline bath containing water-soluble salts of the corresponding organic acid sequestering agents. On the other hand, articles iron plated in the acid baths are more readily rinsed because of their generally lower viscosity.

The presently indicated preferred acid bath is one containing citric acid, e.g., as in bath (b), and even operated at a high pH about 3.5. a

The acid bath (b) can be replaced in that complete operation by any other acid bath respectively specifically identified in any of the foregoing specific baths or any above explained possible modifications of them. Moreover, the method of the invention similarly can be carried out even in a bath of pH 7 just as it can be in any of a pH below that.

However, where it is possible to conduct the electrolytic cleaning in the same bath from which the nascent iron deposit is to be plated out, the bath should be low enough on acid side to enable a practical rate of such cleaning to occur.

It is mentioned above to include a water-soluble iron salt in a bath to facilitate initiating iron electrodeposition in it when the same bath is not used initially to clean the cathode to be plated. In such case, it is possible to include in the acid plating bath an iron salt which while insoluble or of limited solubility in water will dissolve in the acid bath, e.g. ferrous or ferric phosphate.

The acid resistant Duriron alloy included by the third paragraph of this specification among the coarse-surfaced ferrous metals for which the method of the invention is useful, is a ferrous cast alloy which, in addition to iron, contains 14.5% silicon, 0.85% carbon, and 0.65% manganese. Its carbon content includes it also among the high carbon content ferrous metals.

The method of the invention works also with the low carbon ferrous metals such as the low carbon steels which can be cold rolled and shaped by such operations as forging and spinning. However, ordinarily such low carbon ferrous metals readily can be brazed, soldered, or welded.

Thus, the method of the invention is beneficial primarily with those ferrous metals and alloys, with which some difficulty or disadvantage is met in attempts to braze, solder or weld them, so that they generally cannot be brazed, soldered or welded readily or require some special preliminary treatment more difficult, hazardous, and/or costly than merely preliminary electrodeposition of iron.

Herein and in the appended claims, the expression ferrous metal is to be broadly construed as including the ordinary commercial forms of the various irons as well as its common alloys composed highly predominately of iron.

Similarly, the expression metal materia in the longer expression metal material which ordinarily can be fusionjoined readily to a low carbon steel is to be broadly construed to include not only a different metal such as copper or an alloy of it such as brass or bronze, but also a ferrous metal, whether it is an independently formed piece to be fusion-joined, for example, to a casting, or is merely another part of the same ferrous metal which is to be fusion-joined at a crack or seam (as in a butt or lap joint).

While the invention has been explained more extensively by detailed description of certain specific illustrative embodiments of it, it is understood that various modifications and substitutions can be made in any of the thus described embodiments Within the scope of the appended claims which are intended also to include equivalents of any such embodiments.

What is claimed is? v 1. The method of fusion-joining to a coarse-surfaced high carbon content ferrous metal object, a part composed of a fusion-joinable metal which ordinarily can be fusion-joined readily to a low carbon steel, but which may be fusion-joined to a coarse-surfaced high carbon content ferrous metal ordinarily in only a limited way and under specially different conditions, which method comprises cleaning from at least the portion of said ferrous metal object, which will be in the fusion junction, any soil which Could prevent electroplating on such portion an adherent electrodeposit of iron; thereafter electroplating on at least such portion of said ferrous metal a firmly adherent at least masking electrodeposit of iron, while said at least cleaned portion which is to be in the fusion junction is immersed as a cathode in an aqueous iron-plating bath having a pH of from 7 to about 3.0 and containing dissolved therein an organic sequestering agent in an amount substantially sufficient for any iron derivative in the bath to be present as the iron chelate of said sequestering agent; removing the thus iron-plated ferrous metal from said bath and any plating solution adhering to said metal; and thereafter fusion-joining said fusion-joinable metal to the said ferrous metal object at such iron-plated portion and by any simpler fusion-joining method generally readily applicable to fusion-joining to a low carbon steel.

2. A method as claimed in claim 1, wherein the sequestering agent is a hydroxy substituted lower aliphatic compound soluble in the bath which compound includes at least one group -COOR wherein R is a cation which can be replaced by iron at whichever valence it exists in the bath and for it to form a chelate with the ligand portion of the sequestering agent.

3. A method as claimed in claim 2, wherein the hydroxy-substituted lower aliphatic sequestering agent is polyhydroxy.

4. A method as claimed in claim 2, wherein the sequestering agent content of the bath comprises and R is defined as in claim 2.

5. A method as claimed in claim 4, wherein about half of the sequestering agent content of the bath is 'an alkali metal glucoheptonate.

6. A method as claimed in claim 5, wherein the alkali 50 metal is sodium.

7. A method as claimed in claim 5, wherein the pH of the bath is from 7 to about 3.5.

'8. A method as claimed in claim 7, wherein the bath contains also another sequestering agent which is a hydroxy lower aliphatic carboxylic acid having from two to seven carbon atoms, from one to six hydroxyl groups, from one to three carboxyl groups, and is only hydroxy and carboxy substituted.

9. A method as claimed in claim 2, wherein the sequestering agent content of the bath comprises Inc-coon no-ooooa H1 -COOR wherein R is defined as in claim 4.

10. A method as claimed in claim 9, wherein the pH of the bath is from seven to about 3.2.

11. A method as claimed in claim 10, wherein the sequestering agent content consists essentially of citric acid and an alkali metal citrate.

12. A method as claimed in claim 2, wherein prior to direct current deposition of nascent iron on the ferrous metal object, soil is removed from it by subjecting it to the effect of periodic reverse current in the bath for a time sufiicient to remove any soil from at least the portion of its surface, which is to be in the fusion junction; and then subjecting the thus cleaned ferrous metal object as a cathode while in the same bath to direct current to electroplate on it said nascent electrodeposit of iron.

13. A method as claimed in claim 12, wherein the pH of the bath is from seven to about 3.2.

14. The method as claimed in claim 1, wherein the coarse-surfaced high carbon content ferrous metal object is cast iron and the fusion-joinable metal is a member of the class consisting of copper, brass and bronze, and the sequestering agent is citric acid.

References Cited UNITED STATES PATENTS 516,551 3/ 1894 Nourse 204-48 X 1,660,246 2/1928 Wille 29-492 X 1,997,538 4/1935 Armstrong 29-492 X 2,052,862 9/1936 Armstrong. 2,714,089 7/1955 'Meyer 204-48 2,965,551 12/1960 Richard. 2,986,499 5/1961 Wernlund 204-48 40 1,651,403 12/1927 Mougey 29-504 X 1,804,237 5/1931 Steenstrup 29-504 X 2,098,411 11/1937 Hensel 29-492 2,539,247 1/ 1951 Wrighton 29--492 1,571,541 2/1926 Davignon 29-196 2,520,310 8/1950 Frazier 29-196 2,934,820 5/1960 Novak 29-194 X 2,970,068 1/ 1961 Drummond 29-194 3,078,564 2/ 1963 Bourdeau 29-194 FOREIGN PATENTS 698,173 10/ 1953 Great Britain.

OTHER REFERENCES The Electrochemical Society, Preprint 84-25, Oct. 16, 1943, p. 280.

Industrial and Engineering Chemistry, vol. 45, No. 12, December 1953, pp. 2782-2784.

JOHN F. CAMPBELL, Primary Examiner. HYLAND BIZOT, Examiner. 

1. THE METHOD OF FUSION-JOINING TO A COARSE-SURFACED HIGH CARBON CONTENT FERROUS METAL OBJECT, A PART COMPOSED OF A FUSION-JOINABLE METAL WHICH ORDINARILY CAN BE FUSION-JOINED READILY TO A LOW CARBON STEEL, BUT WHICH MAY BE FUSION-JOINED TO A COARSE-SURFACED HIGH CARBON CONTENT FERROUS METAL ORDINARILY IN ONLY A LIMITED WAY AND UNDER SPECIALLY DIFFERENT CONDITIONS, WHICH METHOD COMPRISES CLEANING FROM AT LEAST THE PORTION OF SAID FERROUS METAL OBJECT, WHICH WILL BE IN THE FUSION JUNCTION, ANY SOIL WHICH COULD PREVENT ELECTROPLATING ON SUCH PORTION AN ADHERENT ELECTRODEPOSIT OF IRON; THEREAFTER ELECTROPLATING ON AT LEAST SUCH PORTION OF SAID FERROUS METAL A FIRMLY ADHERENT AT LEAST MASKING ELECTRODEPOSIT OF IRON, WHILE SAID AT LEAST CLEANED PORTION WHICH IS TO BE IN THE FUSION JUNCTION IS IMMERSED AS A CATHODE IN AN AQUEOUS IRON-PLATING BATH HAVING A PH OF FROM 7 TO ABOUT 3.0 AND CONTAINING DISSOLVED THEREIN AN ORGANIC SEQUESTERING AGENT IN AN AMOUNT SUBSTANTIALLY SUFFICIENT FOR ANY IRON DERIVATIVE IN THE BATH TO BE PRESENT AS THE IRON CHELATE OF SAID SEQUESTERING AGENT; REMOVING THE THUS IRON-PLATED FERROUS METAL FROM SAID BATH AND ANY PLATING SOLUTION ADHERING TO SAID METAL; AND THEREAFTER FUSION-JOINING SAID FUSION-JOINABLE METAL TO THE SAID FERROUS METAL OBJECT AT SUCH IRON-PLATED PORTION AND BY ANY SIMPLER FUSION-JOINING METHOD GENERALLY READILY APPLICABLE TO FUSION-JOINING TO A LOW CARBON STEEL. 